Q: You can find all kinds of stories saying that humans share 98 percent of their genetic material with chimps, 80 percent with cats — even 24 percent with the lowly table grape. Is all of this really true?
A.F., of Tilden
A: While such comparisons provide juicy Internet click-bait, knowledgeable scientists seem to agree that such stories are at best simplistic and at worst meaningless because you wind up comparing rutabagas to kumquats rather than oranges to oranges.
Here’s why: It’s inevitable that we’re going to share some genetic material with just about everything from dandelions to gorillas. That’s because scientists believe animals, plants and fungi all share a common ancestor that lived about 1.6 billion years ago, give or take a hundred million or two. Everything that evolved from this ancestor retained part of that original genome so it’s no surprise some similarities are still found today. And it’s no surprise that the higher up the chain you go — comparing pigs and humans, for example, the more similarities you’ll find.
After that, however, all bets are off. The numbers you see probably are comparing only that portion of your DNA that “code for” — or result in the production of — various proteins our bodies need for various biochemical and physiological functions. So, for example, since all mammals need the same types of proteins, it’s only logical they’re going to share a large number of the roughly 20,000 protein-encoding genes. But while 20,000 sounds like a lot, only 1 percent to 2 percent of mammalian genes are thought to encode proteins with similar basic functions. We’re still trying to uncover what many of the other 98 percent do and this is where those comparisons fall apart.
“Depending what it is you are comparing, you can say, ‘Yes, there’s a very high degree of similarity, for example, between a human and a pig protein-coding sequence,” Chris Moran at the University of Sydney once told ABC News. “But if you compare rapidly evolving non-coding sequences from a similar location in the genome, you may not be able to recognize any similarity at all. This means that blanket comparisons of all DNA sequences between species are not very meaningful.”
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